I don't think it's subconscious. It shows up obviously in bezel thickness and radius of corners. When they release a new product the bezel is thick and the corners are very round. As they are able to reduce the bezel size, they also reduce the rounding of the corners. This has the effect of making the last generation look toy-like and the new generation look more serious. They have used this pattern for like 20 years across many product lines.
Cars were like this when they were the conspicious consumption item of choice. Every year, new designs. Not always better, but forever permutation so old parts don't fit and so that the 2 year old models already looked 'dated'. Now we have phones as our way to show our buying power.
This is also the entire model of the fashion industry.
Absolutely, but there's more than one reason to buy a product, and people buying the cheapest and smallest model with last year's technology aren't generally the novelty-seeking "gotta have it" people. Especially people using an iPhone SE in 2020 and raving about how much they love the design. They're not going to win these people over with "new!"
edit: I think this is a very real, but subconscious aspect of Apple culture and it exists across all of the product lines. Phones just happen to be one of their biggest products.